Semiconductor device

ABSTRACT

A method for fabricating a semiconductor device includes: forming a fin-type semiconductor region on a substrate; and introducing an n-type impurity into at least a side of the fin-type semiconductor region by a plasma doping process, thereby forming an n-type impurity region in the side of the fin-type semiconductor region. In the introducing the n-type impurity, when a source power in the plasma doping process is denoted by a character Y [W], the supply of a gas containing the n-type impurity per unit time and per unit volume is set greater than or equal to 5.1×10 −8 /((1.7 2.51 /2 4.51 )×(Y/500)) [mol/(min·L·sec)], and the supply of a diluent gas per unit time and per unit volume is set greater than or equal to 1.7×10 −4 /(20 2.51 /2 4.51 )×(Y/500)) [mol/(min·L·sec)].

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2009-286277 filed on Dec. 17, 2009, the disclosure of which includingthe specification, the drawings, and the claims is hereby incorporatedby reference in its entirety.

BACKGROUND

The present disclosure relates to semiconductor devices and methods forfabricating the same, and more particularly relates to a semiconductordevice having a three-dimensional structure and including a fin-shapedsemiconductor region on a substrate.

In recent years, with increases in the degree of integration,functionality, and speed of semiconductor devices, there is anincreasing demand for miniaturization of semiconductor devices. To meetthe demand, various device structures have been proposed for reducingthe area occupied by transistors over a substrate. Among them, a fieldeffect transistor having a tin-type structure has drawn attention. Thefield effect transistor having the fin-type structure is generallycalled a fin field effect transistor (fin-FET), and has an active regionmade of a semiconductor region (hereinafter referred to as a fin-typesemiconductor region) having a thin-wall (fin) shape perpendicular tothe principal surface of a substrate. In the fin-FET, the side surfacesof the fin-type semiconductor region can be used as channel surfaces,and accordingly the area occupied by transistors over the substrate canbe reduced (see, e.g., Japanese Patent Publication No. 2006-196821 andD. Lenoble et al., “Enhanced performance of PMOS MUGFET via integrationof conformal plasma-doped source/drain extensions,” 2006 Symposium onVLSI Technology Digest of Technical Papers, p. 212).

In Japanese Patent Publication No. 2006-196821, a technique has beenproposed in which ions are implanted into a fin-type silicon region fromoblique directions, thereby forming extension regions andhigh-concentration impurity regions which serve as source/drain regions.When, e.g., an impurity region is formed by such ion implantation fromoblique directions, ions are implanted into side portions of thefin-type silicon region from one direction while ions are implanted intoan upper portion of the fin-type silicon region from two directions.This allows the implant dose of an impurity region in the upper portionof the fin-type silicon region to be twice as large as the implant doseof an impurity region in each of the side portions of the fin-typesilicon region. In other words, it is difficult to form a low-resistanceimpurity region in the side portion of the fin-type silicon region.

Therefore, in recent years, attention has been drawn to the use ofplasma doping in order to dope the side surfaces of a fin-typesemiconductor region with impurities.

A pulsed DC plasma technique has been proposed, as a plasma dopingtechnique for forming an impurity region of a fin-FET, in D. Lenoble etal., “Enhanced performance of PMOS MUGFET via integration of conformalplasma-doped source/drain extensions,” 2006 Symposium on VLSI TechnologyDigest of Technical Papers, p. 212. In the pulsed DC plasma technique, aplasma is generated intermittently, and thus, this technique has anadvantage in that etching of a fin-type semiconductor region can bereduced.

A plasma doping technique using an inductively coupled plasma (ICP)method has been proposed, as a plasma doping technique for forming animpurity region of a fin-FET, in WO 2006/064772. The ICP method has anadvantage in that the surface of a large substrate, such as a waferhaving a diameter of 300 mm, can be uniformly doped by employing alonger time range (doping time) than that used in a pulsed DC plasmamethod.

Japanese Patent Publication No. H01-295416 describes a plasma dopingtechnique for doping the trench side surface, although it is not anobject of the technique to subject the side surfaces of a narrow andfine fin-type semiconductor region to plasma doping.

SUMMARY

As described above, the use of various plasma doping techniques has beenproposed in order to dope the side surfaces of a fin-type semiconductorregion with impurities.

However, when n-type impurities, such as arsenic (As), are to beintroduced into the side surfaces of a fine fin-type semiconductorregion, a low-resistance n-type impurity region cannot be formed in eachof the side surfaces of the fin-type semiconductor region because suchn-type impurities have poor adherence to the fin-type semiconductorregion. This prevents an n-type fin-FET having desired characteristicsfrom being obtained.

It is extremely difficult to use a method in which the side surface of atrench of large dimensions is doped as described in Japanese PatentPublication No. H01-295416 to form an impurity region of a fin-FET. Thereason for this will be described below. Specifically, in such a plasmadoping method for the trench side surface, no consideration is given tocritical technical problems in the formation of a fin-FET, such asamorphization of a fin-type semiconductor region, and chipping of theupper corners of the fin-type semiconductor region. This causes aproblem where large part of the fin-type semiconductor region is madeamorphous, thereby making it difficult to recover crystals even afterannealing, and a problem where the upper corners of the fin-typesemiconductor region are significantly chipped. Consequently, even whensuch a plasma doping method for the trench side surface is used in orderto introduce n-type impurities into side portions of a narrow and finefin-type semiconductor region, and the n-type impurities areelectrically activated by annealing, a low-resistance impurity regioncannot be formed.

In view of the above, it is an object of the present disclosure to allowa low-resistance n-type impurity region to be formed by introducingn-type impurities into side surfaces of a fin-type semiconductor region,thereby achieving an n-type fin semiconductor device having desiredcharacteristics.

In order to achieve the above object, a method for fabricating asemiconductor device according to the present disclosure includes:forming a fin-type semiconductor region on a substrate; and introducingan n-type impurity into at least a side of the fin-type semiconductorregion by a plasma doping process, thereby forming an n-type impurityregion in the side of the fin-type semiconductor region. In theintroducing the n-type impurity, when a source power in the plasmadoping process is denoted by a character Y [W], a supply of a gascontaining the n-type impurity per unit time and per unit volume is setgreater than or equal to 5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)], and a supply of a diluent gas per unit time and perunit volume is set greater than or equal to1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)].

Influences of parameters other than the source power, such as the biasvoltage, on the relationship between the supply of the gas containingthe n-type impurity or the diluent gas per unit time and per unit volumeand the resistance of the n-type impurity region formed in the side ofthe fin-type semiconductor region are substantially negligible.Parameters indicating the substrate temperature, etc., are substantiallyfixed. For example, the substrate temperature is usually fixed atapproximately room temperature. Therefore, the influence of suchparameters does not practically need to be considered.

In the method of the present disclosure, in the introducing the n-typeimpurity, the supply of the gas containing the n-type impurity per unittime and per unit volume may be set greater than or equal to7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and the supplyof the diluent gas per unit time and per unit volume may be set greaterthan or equal to 1.7×10⁻³/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)]. In this case, in the introducing the n-type impurity,the supply of the gas containing the n-type impurity per unit time andper unit volume may be set greater than or equal to8.7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and thesupply of the diluent gas per unit time and per unit volume may be setgreater than or equal to 3.4×10⁻³/((20^(2.51)/2^(4.51))×/(Y/500))[mol/(min·L·sec)].

In the method of the present disclosure, in the introducing the n-typeimpurity, the supply of the gas containing the n-type impurity per unittime and per unit volume may be set less than9.66×10⁻⁶/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)].

In the method of the present disclosure, in the introducing the n-typeimpurity, a chamber volume may be greater than or equal to 30 liters andless than 65 liters, and the supply of the diluent gas per unit time andper unit volume may be set less than or equal to3×10⁻²/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)]. When a triplegate fin-type semiconductor device is fabricated, the supply of thediluent gas per unit time and per unit volume is preferably set lessthan or equal to 2.7×10⁻²/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)]

In the method of the present disclosure, in the introducing the n-typeimpurity, a chamber volume may be greater than or equal to 65 liters andless than or equal to 100 liters, and the supply of the diluent gas perunit time and per unit volume may be set less than or equal to4.66×10⁻³/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)]. When atriple gate fin-type semiconductor device is fabricated, the supply ofthe diluent gas per unit time and per unit volume is preferably set lessthan or equal to 3.8×10⁻³/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)].

In the method of the present disclosure, in the introducing the n-typeimpurity, a pressure during the plasma doping process may be set lessthan or equal to 0.6 Pa. When a double gate fin semiconductor device isfabricated, an upper portion of the fin-type semiconductor region iscovered with a hard mask, thereby relaxing restrictions on chipping (insome cases, hereinafter referred to as erosion) of upper corners of thefin-type semiconductor region due to plasma doping. Therefore, thepressure during plasma doping may be higher than 0.6 Pa. Furthermore,when the method of the present disclosure is used to form a source/drainregion, the pressure during plasma doping can be increased to higherthan 0.6 Pa by performing a process in which the size of a portion ofthe fin-type semiconductor region corresponding to the source/drainregion is increased, etc., even with a triple gate fin semiconductordevice.

In the method of the present disclosure, the gas containing the n-typeimpurity may be AsH₃. A gas containing, e.g., phosphorus (P) may be usedinstead of the gas containing arsenic (As) as the n-type impurity, suchas AsH₃.

In the method of the present disclosure, the diluent gas may be He. Forexample, instead of He, hydrogen (H₂) or neon (Ne) may be used as thediluent gas.

In the method of the present disclosure, the n-type impurity region maybe an extension region or a source/drain region.

In the method of the present disclosure, a width of the fin-typesemiconductor region along a gate width may be less than or equal to 15nm.

A semiconductor device according to the present disclosure includes: afin-type semiconductor region formed on a substrate; and an n-typeimpurity region formed in a side of the fin-type semiconductor region. Aspreading resistance of the n-type impurity region is less than9.0×10⁴Ω.

In the semiconductor device of the present disclosure, the spreadingresistance of the n-type impurity region may be less than or equal to6.3×10⁴Ω. In this case, the spreading resistance of the n-type impurityregion may be less than or equal to 3.6×10⁴Ω.

In the semiconductor device of the present disclosure, the n-typeimpurity region may contain As. The n-type impurity region may contain Pinstead of As.

In the semiconductor device of the present disclosure, the n-typeimpurity region may be an extension region, and a gate electrode may beformed to cover a part of the fin-type semiconductor region adjacent tothe n-type impurity region.

In the semiconductor device of the present disclosure, the n-typeimpurity region may be a source/drain region, a gate electrode may beformed to cover a part of the fin-type semiconductor region apart fromthe n-type impurity region, and an insulative sidewall spacer may beformed to cover a side of the gate electrode and a portion of thefin-type semiconductor region located between the n-type impurity regionand the gate electrode.

In the semiconductor device of the present disclosure, a width of thefin-type semiconductor region along a gate width may be less than orequal to 15 nm.

According to the present disclosure, a low-resistance n-type impurityregion can be formed by introducing an n-type impurity into a side of afin-type semiconductor region, thereby achieving an n-type finsemiconductor device having desired characteristics.

As described above, the present disclosure relates to semiconductordevices and methods for fabricating the same, and is preferable for, inparticular, a semiconductor device having a three-dimensional structureand including a fin-type semiconductor region on a substrate, and amethod for fabricating the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the relationship between the spreadingresistance of the fin top surface of each of samples measured byscanning spreading resistance microscopy (SSRM), and the sheetresistance measured on a bare substrate (single crystal siliconsubstrate) processed under the same condition as the sample subjected toSSRM by a four-point probe technique.

FIG. 2 is a graph illustrating the As profile immediately afterimplantation of As into a bare substrate by plasma doping, and the Asprofile after subsequent annealing.

FIG. 3A is a diagram schematically illustrating the structure of afin-FET with the profile illustrated in FIG. 2 immediately after plasmadoping, and FIG. 3B is a diagram schematically illustrating thestructure of a fin-FET with the profile illustrated in FIG. 2 afterannealing.

FIG. 4A is a diagram schematically illustrating the structure of afin-FET immediately after plasma doping when plasma doping, and hightemperature and short time annealing are used in combination, and FIG.4B is a diagram schematically illustrating the structure of a fin-FETafter high temperature and short time annealing when plasma doping, andhigh temperature and short time annealing are used in combination.

FIGS. 5A-5D are cross-sectional views illustrating process steps in amethod for fabricating a semiconductor device according to an exampleembodiment.

FIGS. 6A-6C are diagrams illustrating the structure of a semiconductordevice according to the example embodiment, in which FIG. 6A is a planview of the semiconductor device, FIG. 6B is a cross-sectional viewtaken along the line A-A in FIG. 6A, and FIG. 6C is a cross-sectionalview taken along the line B-B in FIG. 6A.

FIG. 7 is a graph illustrating the relationship between the total gasflow rate and the spreading resistance of a fin side surface.

FIG. 8 is a graph illustrating the relationship between the total gasflow rate and the spreading resistance of a fin side surface.

FIG. 9 is a graph illustrating the relationship between each of thesupply of AsH₃ molecules and the supply of He atoms, and the spreadingresistance of a fin side surface.

FIG. 10 is a graph illustrating the relationship between each of thesupply of AsH₃ molecules and the supply of He atoms per unit time andper unit volume, and the spreading resistance of a fin side surface.

FIG. 11A is a graph illustrating the internal chamber pressure and theamount of chipping of a fin corner portion, FIG. 11B is a diagramillustrating fin corner portions before plasma doping, and FIGS. 11C-11Eare diagrams illustrating fin corner portions after annealing subsequentto plasma doping.

FIG. 12 is a table collectively illustrating various plasma dopingconditions and results obtained using the plasma doping conditions.

FIG. 13 is a graph illustrating the relationship between the supply ofAsH₃ molecules per unit time and per unit volume and the sheetresistance measured on the flat principal surface of a siliconsubstrate.

FIG. 14 is a graph illustrating the relationship between the supply ofAsH₃ molecules per unit time and per unit volume and the spreadingresistance of a fin side surface.

DETAILED DESCRIPTION

(Setting of Target Spreading Resistance of Fin Side Surface)

Before describing an example embodiment, the results obtained after thepresent inventors investigated the relationship between the spreadingresistance and sheet resistance of the top surface of a fin-typesemiconductor region (hereinafter referred to as the fin top surface)when plasma doping is performed, and the arsenic (As) implantationprofile will be described, and it will be shown that the targetspreading resistance of a side surface of a fin-type semiconductorregion (hereinafter referred to as a fin side surface) can be set basedon these results. Note that unless otherwise specified, the spreadingresistance, the sheet resistance, and the As implantation profile weremeasured using SSRM (2D scanning spreading resistance microscopy), afour-point probe technique, and secondary ion mass spectrometry (SIMS),respectively.

FIG. 1 illustrates the relationship between the spreading resistance ofthe fin top surface of each of samples measured by SSRM, and the sheetresistances measured on a bare substrate (single crystal siliconsubstrate) processed under the same condition as the sample subjected toSSRM by a four-point probe technique. Arsenic in each of the samplessubjected to SSRM and the samples subjected to the four-point probetechnique was electrically activated in monocrystals of silicon underthe same annealing conditions (by spike rapid thermal annealing (RTA) at1025° C.).

As illustrated in FIG. 1, there is a strong correlation between thespreading resistance of the fin top surface and the sheet resistance ofthe corresponding bare substrate (y=0.0159·x+315.73 where the spreadingresistance is denoted by the character x, and the sheet resistance isdenoted by the character y). A possible reason for this is that sincethe resistances were compared to each other in a situation where thediffusion depths were approximately equal under the same annealingconditions, a reduction in the sheet resistance was effected by areduction in resistivity (i.e., the spreading resistance).

FIG. 2 illustrates the As profile immediately after As is implanted intoa bare substrate by plasma doping, and the As profile after subsequentannealing.

As illustrated in FIG. 2, the profile immediately after plasma dopingshows that the implantation depth (the depth at which the Asconcentration immediately after plasma doping is 5×10¹⁸ cm⁻³) is 6.4 nm.By contrast, the profile after annealing shows that the junction depthXj (the depth at which the As concentration after annealing is 5×10¹⁸cm⁻³) is 16.5 nm. It can be seen from the above that the impuritydiffusion length in annealing (the distance to which impurities arediffused by annealing) is approximately 10 nm.

FIG. 3A schematically illustrates the structure of a fin-FET with theprofile illustrated in FIG. 2 immediately after plasma doping, and FIG.3B schematically illustrates the structure of a fin-FET with the profileillustrated in FIG. 2 after annealing. Here, the gate length (Lg) is 22nm, and the fin-FET is directed to a double gate FET having a fin topsurface covered with a hard mask. The fin top surface of such a doublegate FET is covered with a hard mask during plasma doping, and thus,impurities are not implanted into the fin top surface, therebypreventing the fin top surface from functioning as an extension regionor a source/drain region. In other words, impurities are implanted onlyinto the fin side surfaces, and thus, only the fin side surfacesfunction as extension regions or source/drain regions.

When the gate length Lg is 22 nm, the effective channel length ispreferably at least half of the gate length Lg, i.e., approximately 11nm. In this case, the distance from the end of the gate near the sourceto the end of the channel near the source (X₁ in FIG. 3B, i.e., theamount of overlapping of the gate and an extension region) isapproximately half of 11 nm, i.e., approximately 5.5 nm. Here, theimpurity diffusion length in annealing, i.e., 10 nm, which is determinedbased on the profiles illustrated in FIG. 2, is greater than 5.5 nm.Therefore, when arsenic is diffused from the end of the gate near thesource in annealing, the effective channel length is so short that aproblem occurs. To address a situation where the impurity diffusionlength in annealing is long as described above, the structuresillustrated in FIGS. 3A and 3B each include an offset sidewall spacerdescribed in the International Technology Roadmap for Semiconductors(ITRS).

The character X₀ in FIG. 3A (the structure of the double gate FETimmediately after plasma doping) denotes a distance to which ionsimplanted with energy in plasma doping spread (diffuse) to the channel(to immediately below the offset sidewall spacer). However, the ionintroduction energy in plasma doping is lower than the implantationenergy in ion implantation, and thus, the distance X₀ can be set lessthan or equal to 10 nm. Furthermore, the distance X₀ can be set lessthan or equal to 7 nm by lowering the ion introduction energy in plasmadoping. For example, when, under the plasma doping conditions providingthe profiles illustrated in FIG. 2, the bias voltage (Vpp) was set at250 V, the implantation depth in the direction of ion introduction was6.4 nm. In this case, the length to which ions spread in a lateraldirection (in a direction vertical to the direction of ion introduction)will be greater than or equal to half of the implantation depth in thedirection of ion introduction and less than or equal to the implantationdepth, and thus, the distance X₀ will be greater than or equal to 3.2 nmand less than or equal to 6.4 nm (and have a central value of 4.8 nm).

When the width of the offset sidewall spacer is denoted by the characterX_(OSS), the width X_(OSS) is set so that the expression (X₁−X₀+X_(OSS))is equal to the impurity diffusion length in annealing, i.e., 10 nm,which is obtained based on the profiles illustrated in FIG. 2.Specifically, the width X_(OSS) needs to be set greater than or equal to7.7 nm and less than or equal to 10.9 nm because the distance X₁ isapproximately 5.5 nm, the distance X₀ is greater than or equal to 3.2 nmand less than or equal to 6.4 nm, and the expression (X₁−X₀+X_(OSS)) isequal to 10 nm.

As described above, such a double gate FET having a distance X₁ of 5.5nm as illustrated in FIG. 3B can be obtained in the following manner:(i) the length (X₀) of As diffusion to the channel in plasma doping isset greater than or equal to 3.2 nm and less than or equal to 6.4 nm bysetting the bias voltage Vpp in plasma doping at 250 V; (ii) theimpurity diffusion length (X₁−X₀+X_(OSS)) in annealing is adjusted to 10nm by setting the annealing (spike RTA) temperature at 1025° C.; and(iii) the width (X_(OSS)) of the offset sidewall spacer is set greaterthan or equal to 7.7 nm and less than or equal to 10.9 nm.

Incidentally, the resistance of a fin side surface is estimated onlybased on the spreading resistance. By contrast, the resistance of anextension region required for a fin semiconductor device in the ITRS isexpressed in terms of the sheet resistance. Therefore, the presentinventors attempted to convert the maximum drain extension sheetresistance for multi-gate MPU/ASIC (NMOS) described in the ITRS 2008Update to the spreading resistance. Referring to Table FEP4a in the ITRS2008 Update, a required sheet resistance in or before 2014 is notdescribed, and the sheet resistance desired in 2015 is 441 Ω/sq.Subsequently, referring to Table FEP4b, the sheet resistances requiredin 2016, 2017, 2018, 2019, 2020, 2021, and 2022 are 475 Ω/sq., 526Ω/sq., 590 Ω/sq., 642 Ω/sq., 691 Ω/sq., 753 Ω/sq., 868 Ω/sq.,respectively. This shows that the sheet resistance of an extensionregion desired in the ITRS between now and 2022 is in the range of lessthan or equal to 868 Ω/sq. Here, referring to FIG. 1, a sheet resistanceof 868 Ω/sq. corresponds to a spreading resistance of 3.5×10⁴Ω.

Therefore, when the diffusion depth of the fin top surface is equal tothe diffusion depth of a fin side surface, or when the diffusion depthof the fin side surface is greater than that of the fin top surface, thesheet resistance desired in the ITRS is satisfied by setting thespreading resistance of the fin side surface at 3.5×10⁴Ω or less.Specifically, the spreading resistance of the fin side surface ispreferably set less than or equal to 3.5×10⁴Ω.

Next, a case in which high temperature and short time annealing, such aslaser annealing or flash lamp annealing, is used as the above-describedannealing will be described. When such high temperature and short timeannealing is performed, a sheet resistance approximately equal to thesheet resistance obtained by usual annealing can be obtained with afurther reduction in the impurity diffusion length. Therefore, acombination of the above-described plasma doping and high temperatureand short time annealing enables the formation of a fin-FET in which nooffset sidewall spacer is used.

FIG. 4A schematically illustrates the structure of a fin-FET immediatelyafter plasma doping when plasma doping and high temperature and shorttime annealing are used in combination, and FIG. 4B schematicallyillustrates the structure of a fin-FET after high temperature and shorttime annealing when plasma doping and high temperature and short timeannealing are used in combination.

Also in the cases illustrated in FIGS. 4A and 4B, when the length (X₀)of As diffusion to the channel in plasma doping is set greater than orequal to 3.2 nm and less than or equal to 6.4 nm by setting the biasvoltage Vpp in plasma doping at 250 V, and the impurity diffusion length(X₁−X₀) in annealing is reduced to a small value close to approximatelyzero, such a double gate FET as illustrated in FIG. 4B can be obtainedin which the distance X₁ is greater than or equal to 3.2 nm and lessthan or equal to 6.4 nm. A desired distance X₁, i.e., 5.5 nm, fallswithin the above range of distances X₁. For example, when the distanceX₁ is an average value in the range of 3.2-6.4 nm, i.e., 4.8 nm, areduction of the diffusion length (X₁−X₀) in annealing to 0.7 nm canprovide a double gate FET in which the distance X₁ is 5.5 nm.

Next, the structure illustrated in FIG. 4B and the structure illustratedin FIG. 3B will be compared with each other. The As concentration in animpurity region formed by diffusing impurities using annealing is lowerthan that in the impurity region immediately after plasma doping.Furthermore, with an increase in the length of impurity diffusion usingannealing, the resistivity of a leading end portion of a diffusionregion increases. Therefore, in order to reduce the resistance betweenthe source and drain of a FET, the shorter the length of impuritydiffusion using annealing is, the more preferable. Here, in thestructure illustrated in FIG. 4B, the impurity diffusion length (X₁−X₀)in annealing is 0.7 nm, and in the structure illustrated in FIG. 3B, theimpurity diffusion length (X₁−X₀+X_(OSS)) in annealing is 10 nm.Therefore, high temperature and short time annealing is preferablyperformed by adjusting the temperature and the annealing time in hightemperature and short time annealing to provide the same resistivity asthe resistivity obtained by the spike RTA at 1025° C. because thedistance between the source and drain decreases as in the structureillustrated in FIG. 4B, and thus, the resistance between the source anddrain is significantly reduced.

In the structure illustrated in FIG. 4B, the resistivity will be greaterthan the resistivity obtained by the spike RTA at 1025° C. due to areduction in the impurity diffusion length. However, there is no problemas long as an increase in the resistivity is small enough to becompensated for by a resistance reduction arising from a reduction inthe above distance between the source and drain. For example, assumethat a region with As concentrations of greater than or equal to 1×10²⁰cm⁻³ is to be electrically activated by annealing. In this case, whenthe impurity diffusion length in annealing is 0.7 nm, adding 0.7 nm tothe profile illustrated in FIG. 2 immediately after plasma dopingprovides a region which extends to a depth of approximately 5 nm and hasAs concentrations of greater than or equal to 1×10²⁰ cm⁻³ (i.e., theregion to be electrically activated). By contrast, when the impuritydiffusion length in annealing is 10 nm, a region extending to a depth ofapproximately 12.5 nm corresponds to the region with As concentrationsof greater than or equal to 1×10²⁰ cm⁻³ (i.e., the region to beelectrically activated) as shown by the profile illustrated in FIG. 2after annealing. Therefore, when attention is directed toward the lengthof a portion of each of extension regions formed under the gate byplasma doping and annealing, the length in high temperature and shorttime annealing is reduced to approximately 5 nm/12.5 nm=0.4 times thatin usual annealing. Therefore, when high temperature and short timeannealing is used, the resistivity may be increased to 2.5 times thatwhen usual annealing is used. Specifically, when high temperature andshort time annealing is used, the spreading resistance of a fin sidesurface is preferably set less than or equal to 8.8×10⁴Ω.

The following example embodiment will be described based on the targetspreading resistance of the fin side surface set as described above.

Example Embodiment

A method for fabricating a semiconductor device according to an exampleembodiment will be described hereinafter, together with a specificprocess for achieving the target spreading resistance of the fin sidesurface set as described above, with reference to the drawings.

FIGS. 5A-5D are cross-sectional views illustrating process steps in amethod for fabricating a semiconductor device according to this exampleembodiment.

First, as illustrated in FIG. 5A, a semiconductor on insulator (SOI)substrate is prepared which includes a 150-nm-thick insulating layer 12made of, e.g., silicon oxide and formed on a 800-μm-thick supportsubstrate 11 made of, e.g., silicon, and a 50-nm-thick semiconductorlayer made of, e.g., silicon and formed on the insulating layer 12.Thereafter, the semiconductor layer is patterned, thereby forming p-typefin-type semiconductor regions 13 serving as active regions. The width(a) of each of the fin-type semiconductor regions 13 along the gatewidth is, e.g., greater than or equal to 5 nm and less than or equal to15 nm, the width (b) thereof along the gate length is, e.g.,approximately 200 nm, the height (thickness) (c) thereof is, e.g.,approximately 50 nm, and the pitch (d) between each adjacent pair of thefin-type semiconductor regions 13 is, e.g., approximately 1-2 times thewidth (a) (see FIG. 6A).

Next, as illustrated in FIG. 5B, a 3-nm-thick gate insulating film 14made of, e.g., a silicon oxynitride film is formed to cover the outersurfaces of the fin-type semiconductor regions 13, and then, e.g., a60-nm-thick polysilicon film 15A is formed to cover the entire surfaceregion of the support substrate 12.

Next, as illustrated in FIG. 5C, the polysilicon film 15A and the gateinsulating film 14 are sequentially etched, and thus, a gate electrode15 having a width of, e.g., 20 nm along the gate length is formed on thefin-type semiconductor regions 13 with the gate insulating film 14interposed therebetween. Thereafter, n-type impurities are introducedinto upper and side portions of the fin-type semiconductor regions 13 byplasma doping using the gate electrode 15 as a mask, thereby formingfirst n-type impurity regions 17 a and second n-type impurity regions 17b serving as extension regions 17 in the upper and side portions,respectively, of the fin-type semiconductor regions 13. Here, the plasmadoping conditions are such that, for example, the material gas is arsine(AsH₃) diluted with helium (He), the AsH₃ concentration in the materialgas is 0.05% by mass, the total flow rate of the material gas is 440cm³/min (standard state), the internal chamber pressure is 0.5 Pa, thesource power (the plasma-generating high-frequency power) is 500 W, thebias voltage (Vpp) is 250 V, the substrate temperature is 22° C., andthe plasma doping time is 60 seconds.

One of the features of this example embodiment is that when the sourcepower in the plasma doping for forming the extension region 17 isdenoted by the character Y [W], the supply of a gas containing n-typeimpurities (i.e., AsH₃) per unit time and per unit volume is set greaterthan or equal to 5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)], the supply of a diluent gas (i.e., He) per unit timeand per unit volume is set greater than or equal to1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and theinternal chamber pressure is set less than or equal to 0.6 Pa. Thisallows the spreading resistance of the second n-type impurity region 17b corresponding to a portion of the extension region 17 located in aside portion of each of the fin-type semiconductor regions 13 to be setless than 9.0×10⁴Ω, more specifically, less than or equal to 8.8×10⁴Ω.

Next, e.g., a 60-nm-thick insulating film is formed to cover the entiresurface region of the support substrate 12, and then, the insulatingfilm is etched back using anisotropic dry etching, thereby forminginsulative sidewall spacers 16 on the side surfaces of the gateelectrode 15 as illustrated in FIG. 5D. Thereafter, n-type impuritiesare introduced into the upper and side portions of the fin-typesemiconductor regions 13 by plasma doping using the gate electrode 15and the insulative sidewall spacers 16 as masks, thereby forming thirdn-type impurity regions 27 a and fourth n-type impurity regions 27 bserving as source/drain regions 27 in the upper and side portions,respectively, of the fin-type semiconductor regions 13. Here, the plasmadoping conditions are such that, for example, the material gas is arsine(AsH₃) diluted with helium (He), the AsH₃ concentration in the materialgas is 0.05% by mass, the total flow rate of the material gas is 440cm³/min (standard state), the internal chamber pressure is 0.5 Pa, thesource power (the plasma-generating high-frequency power) is 500 W, thebias voltage (Vpp) is 250 V, the substrate temperature is 22° C., andthe plasma doping time is 60 seconds.

One of the features of this example embodiment is that when the sourcepower in the plasma doping for forming the source/drain regions 27 isdenoted by the character Y [W], the supply of a gas containing n-typeimpurities (i.e., AsH₃) per unit time and per unit volume is set greaterthan or equal to 5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)], the supply of a diluent gas (i.e., He) per unit timeand per unit volume is set greater than or equal to1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and theinternal chamber pressure is set less than or equal to 0.6 Pa. Thisallows the spreading resistance of the fourth n-type impurity region 27b corresponding to a portion of the source/drain region 27 located in aside portion of each of the fin-type semiconductor regions 13 to be setless than 9.0×10⁴Ω, more specifically, less than or equal to 8.8×10⁴Ω.

FIGS. 6A-6C are diagrams illustrating the structure of a fin-FET of thisexample embodiment formed as described above, in which FIG. 6A is a planview thereof, FIG. 6B is a cross-sectional view taken along the line A-Ain FIG. 6A, and FIG. 6C is a cross-sectional view taken along the lineB-B in FIG. 6A. FIG. 5D corresponds to a cross-sectional view takenalong the line C-C in FIG. 6A.

As illustrated in FIGS. 6A-6C and 5D, the fin-FET of this exampleembodiment includes a support substrate 11 made of, e.g., silicon, aninsulating layer 12 formed on the support substrate 11 and made of,e.g., silicon oxide, a plurality of fin-type semiconductor regions 13formed on the insulating layer 12, a gate electrode 15 formed on thefin-type semiconductor regions 13 with a gate insulating film 14interposed therebetween, insulative sidewall spacers 16 formed on theside surfaces of the gate electrode 15, extension regions 17 formed inregions of each of the fin-type semiconductor regions 13 lateral to thegate electrode 15, and source/drain regions 27 formed in regions of thefin-type semiconductor region 13 lateral to a combination of the gateelectrode 15 and the insulative sidewall spacers 16. The fin-typesemiconductor regions 13 are disposed on the insulating layer 12 so asto be arranged at regular intervals along the gate width. The gateelectrode 15 is formed astride the fin-type semiconductor regions 13along the gate width. The extension regions 17 each include a firstn-type impurity region 17 a formed in an upper portion of thecorresponding fin-type semiconductor region 13, and a second n-typeimpurity region 17 b formed in a side portion of the fin-typesemiconductor region 13. The source/drain regions 27 each include athird n-type impurity region 27 a formed in an upper portion of thecorresponding fin-type semiconductor region 13, and a fourth n-typeimpurity region 27 b formed in a side portion of the fin-typesemiconductor region 13. A pocket region is neither described norillustrated.

As described above, according to this example embodiment, when thesource power in the plasma doping for forming the extension regions 17is denoted by the character Y [W], the supply of a gas containing n-typeimpurities (i.e., AsH₃) per unit time and per unit volume is set greaterthan or equal to 5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)], the supply of a diluent gas (i.e., He) per unit timeand per unit volume is set greater than or equal to1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and theinternal chamber pressure is set less than or equal to 0.6 Pa. This canreduce the resistance of the second n-type impurity region 17 bcorresponding to a portion of the extension region 17 located in a sideportion of each fin-type semiconductor region 13 (i.e., allows thespreading resistance to be less than 9.0×10⁴Ω), thereby obtaining ann-type fin semiconductor device having desired characteristics.Furthermore, the sheet resistance of the second n-type impurity region17 b formed in a side portion of the fin-type semiconductor region 13can be set substantially equal to or less than the value required for anextension region in the ITRS. Therefore, even when the ratio of thewidth of the second n-type impurity region 17 b to the width of theextension region 17 along the gate width is increased, desiredtransistor characteristics can be achieved.

According to this example embodiment, when the source power in theplasma doping for forming the source/drain regions 27 is denoted by thecharacter Y [W], the supply of a gas containing n-type impurities (i.e.,AsH₃) per unit time and per unit volume is set greater than or equal to5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and thesupply of a diluent gas (i.e., He) per unit time and per unit volume isset greater than or equal to 1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)]. This can reduce the resistance of the fourth n-typeimpurity region 27 b corresponding to a portion of the source/drainregion 27 located in a side portion of each fin-type semiconductorregion 13 (i.e., allows the spreading resistance to be less than9.0×10⁴Ω). Therefore, since the sheet resistance of the fourth n-typeimpurity region 27 b formed in a side portion of the fin-typesemiconductor region 13 can be set substantially equal to that of eachof the extension regions 17, this facilitates moving carriers from thesource/drain regions 27 to the extension regions 17, thereby achievingdesired transistor characteristics. Furthermore, the sheet resistance ofthe fourth n-type impurity region 27 b formed in a side portion of thefin-type semiconductor region 13 can be set substantially equal to orless than the value required for a source/drain region in the ITRS.Therefore, even when the ratio of the width of the fourth n-typeimpurity region 27 b to the width of the corresponding source/drainregion 27 along the gate width is increased, desired transistorcharacteristics can be achieved.

According to this example embodiment, when plasma doping is used to formthe source/drain region 27 in each fin-type semiconductor region 13,this can avoid a problem in which such amorphization of the fin-typesemiconductor region as in the use of ion implantation makes itdifficult to recover crystals even after annealing.

In this example embodiment, when the source power in the plasma dopingfor forming at least either the extension regions 17 or the source/drainregions 27 is denoted by the character Y [W], the supply of a gascontaining n-type impurities (i.e., AsH₃) per unit time and per unitvolume may be set greater than or equal to7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and the supplyof a diluent gas (i.e., He) per unit time and per unit volume may be setgreater than or equal to 1.7×10⁻³/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)]. This can further reduce the resistances of the secondn-type impurity region 17 b and the fourth n-type impurity region 27 bcorresponding to side portions of each fin-type semiconductor region 13(i.e., allows the spreading resistance to be less than or equal to6.3×10⁴Ω), thereby achieving better transistor characteristics.

In this example embodiment, when the source power in the plasma dopingfor forming at least either the extension regions 17 or the source/drainregions 27 is denoted by the character Y [W], the supply of a gascontaining n-type impurities (i.e., AsH₃) per unit time and per unitvolume may be set greater than or equal to8.7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) [mol/(min·L·sec)], and thesupply of a diluent gas (i.e., He) per unit time and per unit volume maybe set greater than or equal to 3.4×10⁻³/((20^(2.51)/2^(4.51))×(Y/500))[mol/(min·L·sec)]. This can further reduce the resistances of the secondn-type impurity region 17 b and the fourth n-type impurity region 27 bcorresponding to side portions of each fin-type semiconductor region 13(i.e., allows the spreading resistance to be less than or equal to3.6×10⁴Ω), thereby achieving better transistor characteristics.

In this example embodiment, a triple gate fin semiconductor device isfabricated which includes extension regions 17 and source/drain regions27 in upper and side portions of each fin-type semiconductor region 13.However, alternatively, a double gate fin semiconductor device may befabricated which includes extension regions 17 and source/drain regions27 in side portions of each fin-type semiconductor region 13.

In this example embodiment, AsH₃ diluted with He is used as the materialgas for plasma doping for forming the extension regions 17 and thesource/drain regions 27. However, the material gas is not limited to anyparticular gas as long as it is a gas containing n-type impurities to beimplanted into the fin-type semiconductor regions 13. For example,instead of AsH₃, other molecules containing arsenic atoms, or othermolecules comprised of arsenic atoms and hydrogen atoms may be used.Alternatively, PH₃, etc., containing phosphorus (P) atoms may be used.Helium is used as the diluent gas for diluting the gas containing then-type impurities. However, instead of helium, any other rare gas, suchas neon (Ne), or hydrogen (H₂) may be used. Alternatively, the gascontaining the n-type impurities does not need to be diluted with adiluent gas.

While, in this embodiment, the plasma generation method is notparticularly limited, e.g., an ICP method or a pulse method may be usedas the plasma generation method.

Restrictions on the supplies of the gas containing the n-type impuritiesand the diluent gas in plasma doping for forming the extension regions17 and the source/drain regions 27 in this example embodiment, thetechnical significance of the restrictions, and the advantages providedby the restrictions will be described hereinafter in detail.

[Reduction in Resistance of Fin Side Surface Resulting from Setting ofTotal Gas Flow Rate]

First, a reduction in the resistance (spreading resistance) of a finside surface resulting from the setting of the total gas flow rate willbe described with reference to the drawings.

FIG. 7 illustrates the influence of variations in the total gas flowrate on the spreading resistances of the fin top surface and a fin sidesurface. Here, the height and width of each of fin-type semiconductorregions for use in samples is 120 nm and 160 nm, respectively, and thedistance between each adjacent pair of the fin-type semiconductorregions is 210 nm. In other words, the distance between the widthwisecenter of each fin-type semiconductor region and the widthwise center ofan adjacent fin-type semiconductor region is 370 nm. Furthermore, acorner portion (hereinafter referred to as the fin corner portion) ofthe fin-type semiconductor region before plasma doping has a radius ofcurvature of 8.7 nm. The reason why the fin corner portion forms not anexact right angle but a shape with curvature even before plasma dopingis that the fin corner portion is, albeit slightly, chipped in dryetching and cleaning process steps before the plasma doping processstep. The plasma doping condition for each of the samples is such thatthe material gas is AsH₃ diluted with He, the AsH₃ concentration in thematerial gas is 0.05-0.8% by mass, the internal chamber pressure is0.35-0.55 Pa, the source power (the plasma-generating high-frequencypower) is 500 W, the bias voltage Vpp is 250 V, the substratetemperature is 22° C., the plasma doping time is 60 seconds, the ICPmethod is used as the plasma generation method, and the chamber volumeis 93 liters (L).

In order to reduce the amount of chipping of the fin corner portion byextremely reducing the amount of ions applied to the fin top surface,the internal chamber pressure is set low for the ICP method, such asless than or equal to 0.55 Pa. For comparison, FIG. 7 also illustrates acomparative example in which the pressure was set higher than 0.6 Pa(specifically, at 0.65 Pa).

A more specific plasma doping condition for each of the samples will bedescribed below. However, common plasma doping conditions for all thesamples are such that the material gas is AsH₃ diluted with He, thesource power (the plasma-generating high-frequency power) is 500 W, thebias voltage Vpp is 250 V, the substrate temperature is 22° C., theplasma doping time is 60 seconds, and the chamber volume is 93 L.

The condition A was set such that the AsH₃ concentration in the materialgas was 0.8% by mass, the internal chamber pressure was 0.35 Pa, and thetotal flow rate of a combination of He and AsH₃ was 30 cm³/min (standardstate).

The condition B was set such that the AsH₃ concentration in the materialgas was 0.8% by mass, the internal chamber pressure was 0.35 Pa, and thetotal flow rate of a combination of He and AsH₃ was 80 cm³/min (standardstate).

The condition C was set such that the AsH₃ concentration in the materialgas was 0.05% by mass, the internal chamber pressure was 0.4 Pa, and thetotal flow rate of a combination of He and AsH₃ was 300 cm³/min(standard state).

The condition D was set such that the AsH₃ concentration in the materialgas was 0.05% by mass, the internal chamber pressure was 0.5 Pa, and thetotal flow rate of a combination of He and AsH₃ was 440 cm³/min(standard state).

The condition E was set such that the AsH₃ concentration in the materialgas was 0.05% by mass, the internal chamber pressure was 0.55 Pa, andthe total flow rate of a combination of He and AsH₃ was 475 cm³/min(standard state).

The condition F was set such that the AsH₃ concentration in the materialgas was 0.05% by mass, the internal chamber pressure was 0.65 Pa, andthe total flow rate of a combination of He and AsH₃ was 540 cm³/min(standard state).

Each sample was subjected to plasma doping under the above correspondingcondition, and then subjected to annealing (specifically, spike RTA at1025° C.), and thereafter, the spreading resistance and erosion on thefin corner portion were measured by SSRM and scanning electronmicroscopy (SEM) observation, respectively. Furthermore, the flatprincipal surfaces of silicon substrates were subjected to plasma dopingunder the above corresponding conditions separately, the siliconsubstrates were then subjected to annealing (specifically, spike RTA at1025° C.), and thereafter, the sheet resistances were measured using afour-point probe technique.

Consequently, under each of the above conditions, the sheet resistance,the spreading resistance of the fin top surface, the spreadingresistance of a fin side surface, and the amount of increase in theradius of curvature of the fin corner portion were obtained as describedbelow.

Under the condition A, the sheet resistance was 777 Ω/sq., the spreadingresistance of the fin top surface was 3.3×10⁴Ω, the spreading resistanceof the fin side surface was 2.5×10⁵Ω, and the amount of increase in theradius of curvature of the fin corner portion was 0.6 nm.

Under the condition B, the sheet resistance was not measured, thespreading resistance of the fin top surface was 4.0×10⁴Ω, the spreadingresistance of the fin side surface was 1.9×10⁵Ω, and the amount ofincrease in the radius of curvature of the fin corner portion was 0.7nm.

Under the condition C, the sheet resistance was 1011 Ω/sq., thespreading resistance of the fin top surface was 3.6×10⁴Ω, the spreadingresistance of the fin side surface was 9.3×10⁴Ω, and the amount ofincrease in the radius of curvature of the fin corner portion was 0.9nm.

Under the condition D, the sheet resistance was 550 Ω/sq., the spreadingresistance of the fin top surface was 1.3×10⁴Ω, the spreading resistanceof the fin side surface was 3.6×10⁴Ω, and the amount of increase in theradius of curvature of the fin corner portion was 1.2 nm.

Under the condition E, the sheet resistance was 500 Ω/sq., the spreadingresistance of the fin top surface was 1.1×10⁴Ω, the spreading resistanceof the fin side surface was 3.3×10⁴Ω, and the amount of increase in theradius of curvature of the fin corner portion was 2.0 nm.

Under the condition F, the sheet resistance was 478 Ω/sq., the spreadingresistance of the fin top surface was 8.2×10³Ω, the spreading resistanceof the fin side surface was 2.6×10⁴Ω, and the amount of increase in theradius of curvature of the fin corner portion was 5.7 nm.

FIG. 7 which is a graph providing a summary of the above results showsthat the boundary value (threshold) of the total gas flow rate isapproximately 420 cm³/min (standard state), arsenic is less likely toenter the fin side surfaces in the range of total gas flow rates of lessthan the threshold, and arsenic tends to enter the fin side surfaces inthe range of total gas flow rates of greater than or equal to thethreshold. Specifically, the trend in the rate of decrease in thespreading resistance with an increase in the total gas flow rate in therange of total gas flow rates of less than the threshold is differentfrom that in the range of total gas flow rates of greater than or equalto the threshold. In FIG. 7, the symbol  denotes the spreadingresistance of a fin side surface, and the symbol ▪ denotes the spreadingresistance of the fin top surface.

Specifically, while, in the range of total gas flow rates of less thanthe threshold, an increase in the total gas flow rate enables theintroduction of a significant amount of arsenic into a fin side surface,the absolute value itself of the amount of the introduced arsenic isinsufficient, and thus, the spreading resistance of a fin side surfaceis high. By contrast, in the range of total gas flow rates of greaterthan or equal to the threshold, even with an increase in the total gasflow rate, the rate of increase in the amount of the introduced arsenicis lower than that in the range of total gas flow rates of less than thethreshold. However, the absolute value of the amount of the introducedarsenic reaches the practical level, and thus, the spreading resistanceof a fin side surface is low. Specifically, the spreading resistance ofthe fin side surface can be reduced to a low level of less than or equalto 4×10⁴Ω by setting the total gas flow rate at approximately 420cm³/min (standard state) or more. Furthermore, the proportionaldistribution of the result under the condition D and the result underthe condition E shows that the spreading resistance of the fin sidesurface can be reduced to 3.5×10⁴Ω or less, i.e., the most preferablelevel satisfying the sheet resistance desired in the ITRS, by settingthe total gas flow rate at 452 cm³/min (standard state) or more.

[Threshold Total Gas Flow Rate]

In FIG. 7, the threshold at which the trend of As tending to enter thefin side surfaces changes was determined without consideration of thefact that while the AsH₃ concentration under the conditions C, D, E, andF was 0.05% by mass, the AsH₃ concentration under the conditions A and Bwas 0.8% by mass. However, if the AsH₃ concentration under theconditions A and B had been 0.05% by mass, the spreading resistance of afin side surface provided by each of the conditions A and B would havebeen clearly higher than the above-mentioned corresponding value.Therefore, when the AsH₃ concentrations under the conditions A-F arestandardized at 0.05% by mass, it is estimated that the threshold totalgas flow rate at which the trend of As tending to enter the fin sidesurfaces changes will fall within the range of total gas flow rates ofgreater than 300 cm³/min (standard state) and less than or equal to 400cm³/min (standard state) as illustrated in FIG. 8.

[Threshold Supply of AsH₃ Molecules and Threshold Supply of He Atoms]

Next, two parameters indicating the AsH₃ concentration and the AsH₃ flowrate were used in the characteristic equation of gas so as to be unifiedinto one parameter as the supply of AsH₃ molecules (mol/min), and twoparameters indicating the He concentration and the He flow rate wereused in the characteristic equation of gas so as to be unified into oneparameter as the supply of He atoms (mol/min), thereby evaluating theease of introducing As into the fin side surfaces in terms of newparameters, i.e., the supply of AsH₃ molecules and the supply of Heatoms. The evaluation results will be described below.

Specifically, the condition A was such that the AsH₃ concentration inthe material gas was 0.8% by mass, the He concentration was 99.2% bymass, and the total flow rate of a combination of He and AsH₃ was 30cm³/min (standard state). This condition is equal to a situation wherethe supply of AsH₃ molecules is 5.54×10⁻⁷ mol/min, and the supply of Heatoms is 1.34×10⁻³ mol/min.

The condition B was such that the AsH₃ concentration in the material gaswas 0.8% by mass, the He concentration was 99.2% by mass, and the totalflow rate of a combination of He and AsH₃ was 80 cm³/min (standardstate). This condition is equal to a situation where the supply of AsH₃molecules is 1.48×10⁻⁶ mol/min, and the supply of He atoms is 3.57×10⁻³mol/min.

The condition C was such that the AsH₃ concentration in the material gaswas 0.05% by mass, the He concentration was 99.95% by mass, and thetotal flow rate of a combination of He and AsH₃ was 300 cm³/min(standard state). This condition is equal to a situation where thesupply of AsH₃ molecules is 3.44×10⁻⁷ mol/min, and the supply of Heatoms is 1.34×10⁻² mol/min.

The condition D was such that the AsH₃ concentration in the material gaswas 0.05% by mass, the He concentration was 99.95% by mass, and thetotal flow rate of a combination of He and AsH₃ was 440 cm³/min(standard state). This condition is equal to a situation where thesupply of AsH₃ molecules is 5.04×10⁻⁷ mol/min, and the supply of Heatoms is 1.96×10⁻² mol/min.

The condition E was such that the AsH₃ concentration in the material gaswas 0.05% by mass, the He concentration was 99.95% by mass, and thetotal flow rate of a combination of He and AsH₃ was 475 cm³/min(standard state). This condition is equal to a situation where thesupply of AsH₃ molecules is 5.44×10⁻⁷ mol/min, and the supply of Heatoms is 2.12×10⁻² mol/min.

The condition F was such that the AsH₃ concentration in the material gaswas 0.05% by mass, the He concentration was 99.95% by mass, and thetotal flow rate of a combination of He and AsH₃ was 540 cm³/min(standard state). This condition is equal to a situation where thesupply of AsH₃ molecules is 6.19×10⁻⁷ mol/min, and the supply of Heatoms is 2.41×10⁻² mol/min.

In order to examine the influence of variations in the supply of AsH₃molecules on the amount of As introduced into a fin side surface whenthe supply of He atoms are set at approximately the same value, sampleswere evaluated further using the condition G.

Here, the condition G was such that the AsH₃ concentration in thematerial gas was 0.025% by mass, the internal chamber pressure is 0.55Pa, and the total flow rate of a combination of He and AsH₃ was 475cm³/min (standard state). Specifically, since the condition G was suchthat the AsH₃ concentration in the material gas was 0.025% by mass, theHe concentration was 99.975% by mass, and the total flow rate of acombination of He and AsH₃ was 475 cm³/min (standard state), thiscondition is equal to a situation where the supply of AsH₃ molecules is2.72×10⁻⁷ mol/min, and the supply of He atoms is 2.12×10⁻² mol/min.

When the condition G was used, the sheet resistance, the spreadingresistance of the fin top surface, the spreading resistance of a finside surface, and the amount of increase in the radius of curvature of afin corner were 882 Ω/sq., 2.9×10⁴Ω, 1.49×10⁵Ω, and 1.6 nm,respectively.

The results obtained under the conditions A-F and the result obtainedunder the condition G are estimated together below. FIG. 9 is a graphproviding a summary of the results obtained under the conditions A-G.

As illustrated in FIG. 9, under each of the conditions D, E, and F, thespreading resistance of a fin side surface is low, such as less than orequal to 3.6×10⁴Ω. By contrast, under each of the conditions A, B, C,and G, the spreading resistance of a fin side surface is higher than9×10⁴Ω. As such, when the condition D, E, or F is used, the spreadingresistance of the fin side surface can be reduced to less than or equalto half the spreading resistance when the condition A, B, C, or G isused.

As illustrated in FIG. 9, comparisons between the cases where theconditions D, E, and F were used and the case where the condition G wasused show that unless the supply of AsH₃ molecules is greater than acertain threshold, the spreading resistance of a fin side surface is notreduced even with approximately the same supply of He atoms. Here, thecomparisons and the result under the condition C show that when thesupply of AsH₃ molecules is at least greater than or equal to 3.5×10⁻⁷mol/min, the spreading resistance of the fin side surface can be reducedto less than or equal to 9×10⁴Ω. Furthermore, the proportionaldistribution of the result under the condition C and the result underthe condition D shows that when the supply of AsH₃ molecules is greaterthan or equal to 4.3×10⁻⁷ mol/min, the spreading resistance of the finside surface can be reduced to less than or equal to 6.3×10⁴Ω. Theresult under the condition D shows that when the supply of AsH₃molecules is greater than or equal to 5.0×10⁻⁷ mol/min, the spreadingresistance of the fin side surface can be reduced to less than or equalto 3.6×10⁴Ω.

Furthermore, as illustrated in FIG. 9, comparisons between the caseswhere the conditions D, E, and F were used and the case where thecondition A was used show that unless the supply of He atoms is greaterthan a certain threshold, the spreading resistance of a fin side surfaceis not reduced even with approximately the same supply of AsH₃molecules. Here, the comparisons and the result under the condition Bshow that when the supply of He atoms is at least greater than or equalto 3.6×10⁻³ mol/min, the spreading resistance of the fin side surfacecan be reduced to less than or equal to 9×10⁴Ω. Furthermore, theproportional distribution of the result under the condition B and theresult under the condition D shows that when the supply of He atoms isgreater than or equal to 1.16×10⁻² mol/min, the spreading resistance ofthe fin side surface can be reduced to less than or equal to 6.3×10⁴Ω.The result under the condition D shows that when the supply of He atomsis greater than or equal to 1.96×10⁻² mol/min, the spreading resistanceof the fin side surface can be reduced to less than or equal to3.6×10⁴Ω.

Here, when attention is directed toward the result under the conditionB, the supply of AsH₃ molecules under the condition B is much greaterthan the lower limit of the above-described strictest range of criteria(in which the spreading resistance of the fin side surface is reduced toless than or equal to 3.6×10⁴Ω) of greater than or equal to 5.0×10⁻⁷mol/min. However, in this case, the spreading resistance of the fin sidesurface is high, such as 1.9×10⁵Ω. This shows that even when only thesupply of AsH₃ molecules meets the criteria range, the spreadingresistance of the fin side surface cannot be reduced. The reason why thespreading resistance of the fin side surface under the condition B ishigh as described above is that the supply of He atoms is 3.57×10⁻³mol/min which is below the lower limit of the above-described strictestrange of criteria. In other words, the supply of He atoms isinsufficient. By contrast, since the condition D was such that thesupply of AsH₃ molecules is 5.04×10⁻⁷ mol/min, and the supply of Heatoms is 1.96×10⁻² mol/min, the supply of AsH₃ molecules is above thelower limit of the above-described strictest range of criteria, i.e.,5.0×10⁻⁷ mol/min, and simultaneously, the supply of He atoms also meetsthe lower limit of the above-described strictest range of criteria,i.e., 1.96×10⁻² mol/min. Therefore, the spreading resistance of the finside surface can be low, such as 3.57×10⁴Ω.

When, as described above, the supply of AsH₃ molecules and the supply ofHe atoms are both greater than or equal to respective certainthresholds, this facilitates introducing As into the fin side surfaces.Specifically, when the supply of AsH₃ molecules is greater than or equalto 5.0×10⁻⁷ mol/min, and the supply of He atoms is greater than or equalto 1.96×10⁻² mol/min, the spreading resistance of a fin side surface canbe lowest, such as less than or equal to 3.6×10⁴Ω. Furthermore, when thesupply of AsH₃ molecules is greater than or equal to 4.3×10⁻⁷ mol/min,and the supply of He atoms is greater than or equal to 1.16×10⁻²mol/min, the spreading resistance of the fin side surface can be low,such as less than 6.3×10⁴Ω. Moreover, when the supply of AsH₃ moleculesis greater than or equal to 3.5×10⁻⁷ mol/min, and the supply of He atomsis greater than or equal to 3.6×10⁻³ mol/min, this allows the spreadingresistance of the fin side surface to be close to the upper limit of thepractically allowable range of less than 9.0×10⁴Ω.

[Threshold Supply of AsH₃ Molecules and Threshold Supply of He Atoms PerUnit Time and Per Unit Volume]

Next, the results obtained by estimating the range of the conditionsfacilitating introducing As into the fin side surfaces in considerationof the chamber volume and the internal chamber pressure will bedescribed.

Specifically, first, the supply of AsH₃ molecules (mol/min) and thesupply of He atoms (mol/min) are each divided by the chamber volume(unit: liter (L)), and the thus-obtained parameters indicating thesupply of AsH₃ molecules (mol/(min·L)) per unit volume and the supply ofHe atoms (mol/(min·L)) per unit volume were introduced.

Next, in order to make estimation in consideration of differentpressures (internal chamber pressures) among samples, consideration wasgiven to the time between the supply of a gas into the chamber and theemission of the gas (gas residence time). Here, the gas residence time T(second) was calculated by using the equation obtained by substituting 1(cm³/min (standard state))=1.27×10⁻² (Torr·L/sec) derived from 1(Torr·L/sec)=0.133 (Pa·m³/sec) and 1 (Pa·m³/sec)=592 (cm³/min (standardstate)) into T=V·P/Q (where the character V denotes the chamber volume(L), the character P denotes the pressure (Torr), and the character Qdenotes the total gas flow rate (Torr·L/sec)), i.e., T=V·P/(1.27×10⁻²·F)(where the character F denotes the total gas flow rate (cm³/min(standard state)). Then, the supply of AsH₃ molecules (mol/(min·L)) perunit volume and the supply of He atoms (mol/(min·L)) per unit volume areeach divided by the gas residence time, and the thus-obtained parametersindicating the supply of AsH₃ molecules (mol/(min·L·sec)) per unit timeand per unit volume and the supply of He atoms (mol/(min·L·sec)) perunit time and per unit volume were introduced. These parameters enableidentification of the range of the conditions facilitating introducingAs into the fin side surfaces, and the range of the conditions is notdependent on the chamber volume and the chamber pressure.

The gas residence time, the supply of AsH₃ molecules per unit time andper unit volume, and the supply of He atoms per unit time and per unitvolume under each of the above conditions will be described below.

Under the condition A, the gas residence time was 0.641 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 9.30×10⁻⁹mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 2.25×10⁻⁵ mol/(min·L·sec).

Under the condition B, the gas residence time was 0.240 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 6.63×10⁻⁸mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 1.60×10⁻⁴ mol/(min·L·sec).

Under the condition C, the gas residence time was 0.073 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 5.05×10⁻⁸mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 1.97×10⁻³ mol/(min·L·sec).

Under the condition D, the gas residence time was 0.062 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 8.69×10⁻⁸mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 3.38×10⁻³ mol/(min·L·sec).

Under the condition E, the gas residence time was 0.064 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 9.20×10⁻⁸mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 3.59×10⁻³ mol/(min·L·sec).

Under the condition F, the gas residence time was 0.066 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 1.01×10⁻⁷mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 3.92×10⁻³ mol/(min·L·sec).

Under the condition G, the gas residence time was 0.064 seconds, thesupply of AsH₃ molecules per unit time and per unit volume was 4.6×10⁻⁸mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume was 3.59×10⁻³ mol/(min·L·sec).

FIG. 10 is a graph providing a summary of the results obtained under theconditions A-G by using the supply of AsH₃ molecules and the supply ofHe atoms per unit time and per unit volume as parameters.

As illustrated in FIG. 10, comparisons between the results obtainedunder the conditions D, E, and F and the result obtained under thecondition G show that unless the supply of AsH₃ molecules per unit timeand per unit volume is greater than or equal to a certain threshold, asufficient amount of arsenic cannot be introduced into a fin sidesurface even with approximately the same supply of He atoms per unittime and per unit volume.

Furthermore, as illustrated in FIG. 10, comparisons between the resultsobtained under the conditions D, E, and F and the result obtained underthe condition B show that unless the supply of He atoms per unit timeand per unit volume is greater than or equal to a certain threshold, asufficient amount of arsenic cannot be introduced into a fin sidesurface even with approximately the same supply of AsH₃ molecules perunit time and per unit volume.

Specifically, the result under the condition D shows that when thesupply of AsH₃ molecules per unit time and per unit volume is greaterthan or equal to approximately 8.7×10⁻⁸ mol/(min·L·sec), and the supplyof He atoms per unit time and per unit volume is greater than or equalto approximately 3.4×10⁻³ mol/(min·L·sec), the spreading resistance of afin side surface can be lowest, such as less than or equal to 3.6×10⁴Ω.

Furthermore, it can be seen that when the supply of AsH₃ molecules perunit time and per unit volume is set greater than or equal toapproximately 7.0×10⁻⁸ mol/(min·L·sec) based on the proportionaldistribution of the result under the condition D and the result underthe condition C, and the supply of He atoms per unit time and per unitvolume is set greater than or equal to approximately 1.7×10⁻³mol/(min·L·sec) based on the proportional distribution of the resultunder the condition D and the result under the condition B, thespreading resistance of a fin side surface can be low, such as less thanor equal to 6.3×10⁴Ω.

Moreover, when the supply of AsH₃ molecules per unit time and per unitvolume is set greater than or equal to approximately 5.1×10⁻⁸mol/(min·L·sec) based on the result under the condition C, and thesupply of He atoms per unit time and per unit volume is set greater thanor equal to approximately 1.7×10⁻⁴ mol/(min·L·sec) based on the resultunder the condition B, this allows the spreading resistance of the finside surface to be close to the upper limit of the practically allowablerange of less than 9.0×10⁴Ω.

[Reduction in Amount of Chipping of Fin Corner Portion]

Next, the relationship between the internal chamber pressure and theamount of chipping of a fin corner portion will be described withreference to the drawings.

FIG. 11A illustrates the relationship between the internal chamberpressure and the amount of chipping of the fin corner portion under eachof the above conditions. Here, chipping of a fin corner portion due toplasma doping is referred to as erosion.

As described above, each of the conditions D and E was such that theinternal chamber pressure was set low, i.e., at 0.5-0.55 Pa. Asillustrated in FIG. 11B, the radius of curvature of a fin corner portionbefore plasma doping was approximately 9.3 nm. By contrast, asillustrated in FIGS. 11C and 11D, the radius of curvature of a fincorner portion after annealing subsequent to plasma doping under thecondition D was approximately 10.5 nm, and the radius of curvature of afin corner portion after annealing subsequent to plasma doping under thecondition E was approximately 11.3 nm. Therefore, as illustrated in FIG.11A, the use of either of the conditions D and E reduces the amount ofincrease in the radius of curvature to less than or equal to 2 nm. Thisadvantage is provided by setting the internal chamber pressure at a lowpressure of less than or equal to 0.6 Pa. As described above, when thecondition D or E is used, a desired amount of arsenic can be introducedinto a fin side surface.

By contrast, assume that when arsenic ions are implanted into fin-typesemiconductor regions, a plurality of fin-type semiconductor regions arealigned. In this case, a small implantation angle (e.g., an implantationangle of less than or equal to 25 degrees) is used. In such a case, whenthe As implantation energy is high, the amount of chipping of a fincorner portion is large, such as approximately 2.4-4.2 nm, and even whenthe As implantation energy is low, the amount of chipping of a fincorner portion is approximately 2.2 nm.

Therefore, the above condition D or E allowing the amount of chipping(the amount of increase in the radius of curvature) to be less than orequal to 2 nm is preferably used to form extension regions of a fin-FET(see FIG. 7).

By contrast, under the condition F, the radius of curvature of a fincorner portion after plasma doping using the condition F and annealingwas approximately 15.0 nm as illustrated in FIG. 11E due to the factthat the pressure was set slightly higher, such as 0.65 Pa. Here, since,as described above, the radius of curvature of a fin corner portionbefore plasma doping was 9.3 nm, the amount of increase in the radius ofcurvature when the condition F was used reaches a value as large as 5.7nm as illustrated in FIG. 11A. It is difficult to use the conditioncausing such a large amount of chipping to form extension regions (seeFIG. 7). However, when such a condition is used to form source/drainregions, this presents no particular problem as long as a process inwhich the size of portions of the fin-type semiconductor regionscorresponding to the source/drain regions is increased, etc., isperformed (see FIG. 7).

As described above, when the condition F is used, a desired amount of Ascan be introduced into a fin side surface. However, the amount ofchipping of a fin corner portion under the condition F is large enoughto make it difficult to use the condition F to form extension regions.

The internal chamber pressures under the conditions A, B, and C are setat low levels of less than or equal to 0.6 Pa, such as 0.35-0.4 Pa, andthus, as illustrated in FIG. 11A, the use of any one of the conditionsA, B, and C reduces the amount of chipping of a fin corner portion to avery low level, such as less than or equal to 1 nm. However, asdescribed above, the use of any one of the conditions A, B, and Cprevents a desired amount of As from being introduced into a fin sidesurface.

As described above, in order to provide low-resistance extension regionswhile reducing the amount of chipping of a fin corner portion in thefabrication of a fin-FET, the supply of AsH₃ molecules per unit time andper unit volume is preferably set greater than or equal to approximately5.1×10⁻⁸ mol/(min·L·sec), the supply of He atoms per unit time and perunit volume is preferably set greater than or equal to approximately1.7×10⁻⁴ mol/(min·L·sec), and the internal chamber pressure ispreferably set less than or equal to 0.6 Pa.

In the fabrication of a double gate fin semiconductor device, an upperportion of a fin-type semiconductor region is covered with a hard mask,thereby relaxing restrictions on chipping (erosion) of upper corners ofthe fin-type semiconductor region due to plasma doping. Therefore, thepressure during plasma doping may be higher than 0.6 Pa. In theformation of source/drain regions, when a process in which the size ofportions of the fin-type semiconductor regions corresponding to thesource/drain regions is increased, etc., is performed as describedabove, the pressure during plasma doping can be higher than 0.6 Pa evenwith a triple gate fin semiconductor device.

[Influence of Source Power on Threshold Supply of AsH₃ Molecules andThreshold Supply of He Atoms]

Next, the results obtained by estimating the influence of the sourcepower (SP) on the amount of As introduced into a fin side surface willbe described.

A sample was evaluated using the condition H under which the magnitudeof the source power is different from that under each of the aboveconditions A-G. The condition H was set such that the AsH₃ concentrationin the material gas was 0.05% by mass, the internal chamber pressure was0.55 Pa, the total flow rate of a combination of He and AsH₃ was 475cm³/min (standard state), and the SP was 250 W.

Specifically, the sample was subjected to plasma doping under thecondition H, and then subjected to annealing (specifically, spike RTA at1025° C.), and thereafter, the spreading resistance and erosion on a fincorner portion were measured by SSRM and SEM observation, respectively.Furthermore, the flat principal surface of a silicon substrate wassubjected to plasma doping under the condition H separately, the siliconsubstrate was then subjected to annealing (specifically, spike RTA at1025° C.), and thereafter, the sheet resistance was measured using afour-point probe technique.

Consequently, under the condition H, the sheet resistance, the spreadingresistance of the fin top surface, the spreading resistance of a finside surface, and the amount of increase in the radius of curvature of afin corner portion were obtained as described below.

Specifically, under the condition H, the sheet resistance was 524 Ω/sq.,the spreading resistance of the fin top surface was 2.2×10⁴Ω, thespreading resistance of the fin side surface was 5.53×10⁴Ω, and theamount of increase in the radius of curvature of the fin corner portionwas 1.5 nm.

Here, when the condition H is compared with the condition E, theseconditions are different only in SP. Specifically, while the SP underthe condition E was 500 W, the SP under the condition H was set low,such as half of the SP under the condition E, i.e., 250 W. Next, theresult under the condition H and the result under the condition E arecompared with each other. While the sheet resistance of the fin topsurface under the condition H was 524 Ω/sq., the sheet resistance of thefin top surface under the condition E was 500 Ω/sq. Thus, the sheetresistance of the fin top surface under the condition E is approximately5% lower than that under the condition H. Furthermore, while thespreading resistance of the fin top surface under the condition H was2.2×10⁴Ω, the spreading resistance of the fin top surface under thecondition E was 1.1×10⁴Ω. Thus, the spreading resistance of the fin topsurface under the condition E is approximately 50% lower than that underthe condition H. Moreover, while the spreading resistance of a fin sidesurface under the condition H was approximately 5.5×10⁴Ω, the spreadingresistance of a fin side surface under the condition E was 3.3×10⁴Ω.Thus, the spreading resistance of the fin side surface under thecondition E is approximately 40% lower than that under the condition H.

The above results show that with an increase in the SP, the amount of Asintroduced into each of the fin side surfaces and the fin top surfaceincreases. This indicates that with an increase in the SP, the supply ofthe material gas (AsH₃ and He) needed to introduce a desired amount ofAs into a fin side surface decreases.

The above-described comparison between the result under the condition Hand the result under the condition E shows that the spreading resistanceof a fin side surface is reduced by 40% (i.e., to 0.6 times its originalvalue) by doubling the SP from 250 W to 500 W. When the supply of thematerial gas is set at the same value, an increase in SP will increase asubstantial supply of the material gas. Therefore, when the SP is set at1000 W, the spreading resistance of the fin side surface will be furtherreduced by 40% of the spreading resistance when the SP is set at 500 W(i.e., to 0.6 times the spreading resistance when the SP is set at 500W).

By contrast, referring to the supplies of the material gases in FIG. 10,when the supply of AsH₃ molecules per unit time and per unit volume isincreased from 5.1×10⁻⁸ mol/(min·L·sec) to 8.7×10⁻⁸ mol/(min·L·sec),i.e., 1.7 times its original value, and the supply of He atoms per unittime and per unit volume is increased from 1.7×10⁻⁴ mol/(min·L·sec) to3.4×10⁻³ mol/(min·L·sec), i.e., 20 times its original value, thisreduces the spreading resistance of a fin side surface from 9.0×10⁴Ω to3.6×10⁴Ω by 60% (i.e., to 0.4 times its original value).

Specifically, while the spreading resistance of a fin side surface canbe reduced by 40% (to 0.6 times its original value) by doubling the SP,the spreading resistance of the fin side surface can be reduced by 60%(to 0.4 times its original value) by increasing the supply of AsH₃molecules per unit time and per unit volume to 1.7 times its originalvalue and increasing the supply of He atoms per unit time and per unitvolume to 20 times its original value.

Here, a case where the spreading resistance of a fin side surface isreduced by 90% (to 0.1 times its original value) by adjusting the SP,the supply of AsH₃ molecules per unit time and per unit volume, and thesupply of He atoms per unit time and per unit volume will be considered.

The equation “0.6^(A)=0.1” holds, and thus, A≈4.51. Therefore, thespreading resistance of a fin side surface can be reduced by 90% (to 0.1times its original value) by increasing the SP to 2^(4.51) times itsoriginal value. By contrast, the equation “0.4^(B)=0.1” holds, and thus,B≈2.51. Therefore, the spreading resistance of the fin side surface canbe reduced by 90% (to 0.1 times its original value) by increasing thesupply of AsH₃ molecules per unit time and per unit volume to 1.7^(2.51)times its original value and increasing the supply of He atoms per unittime and per unit volume to 20^(2.51) times its original value.Therefore, the increase of the SP to 2^(4.51) times the original SP isequal to a situation where the supply of AsH₃ molecules per unit timeand per unit volume and the supply of He atoms per unit time and perunit volume are increased to 1.7^(2.51) times and 20^(2.51) times,respectively, their corresponding original values.

Next, a case where the SP is Y (W) will be considered. The source powerY (W) is Y/500 times as high as 500 W. Therefore, the setting of the SPat Y/500 times its original value is equal to the following situation:the supply of AsH₃ molecules per unit time and per unit volume is(1.7^(2.51)/2^(4.51))×(Y/500) times as large as its original value; andthe supply of He atoms per unit time and per unit volume is(20^(2.51)/2^(4.51))×(Y/500) times as large as its original value.

Therefore, the supply of AsH₃ molecules per unit time and per unitvolume needed to allow the spreading resistance to be less than 9.0×10⁴Ωwhen the SP is Y (W) is 5.1×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500))(mol/(min·L·sec)), which is obtained by dividing the supply of AsH₃molecules per unit time and per unit volume needed to allow thespreading resistance to be less than 9.0×10⁴Ω when the SP is 500 W,i.e., 5.1×10⁻⁸ mol/(min·L·sec), by (1.7^(2.51)/2^(4.51))×(Y/500). Thesupply of He atoms per unit time and per unit volume needed to allow thespreading resistance to be less than 9.0×10⁴Ω when the SP is Y (W) is1.7×10⁻⁴/((20^(2.51)/2^(4.51))×(Y/500)) (mol/(min·L·sec)), which isobtained by dividing the supply of He atoms per unit time and per unitvolume needed to allow the spreading resistance to be less than 9.0×10⁴Ωwhen the SP is 500 W, i.e., 1.7×10⁻⁴ mol/(min·L·sec), by(20^(2.51)/2^(4.51))×(Y/500). The use of the above supply of AsH₃molecules per unit time and per unit volume and the above supply of Heatoms per unit time and per unit volume allows the spreading resistanceof a fin side surface to be close to the upper limit of the practicallyallowable range of less than 9.0×10⁴Ω.

Similarly, the supply of AsH₃ molecules per unit time and per unitvolume needed to allow the spreading resistance to be less than or equalto 6.3×10⁴Ω when the SP is Y (W) is7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) (mol/(min·L·sec)), which isobtained by dividing the supply of AsH₃ molecules per unit time and perunit volume needed to allow the spreading resistance to be less than orequal to 6.3×10⁴Ω when the SP is 500 W, i.e., 7×10⁻⁸ mol/(min·L·sec), by(1.7^(2.51)/2^(4.51))×(Y/500). The supply of He atoms per unit time andper unit volume needed to allow the spreading resistance to be less thanor equal to 6.3×10⁴Ω when the SP is Y (W) is1.7×10⁻³/((20^(2.51)/2^(4.51))×(Y/500)) (mol/(min·L·sec)), which isobtained by dividing the supply of He atoms per unit time and per unitvolume needed to allow the spreading resistance to be less than 6.3×10⁴Ωwhen the SP is 500 W, i.e., 1.7×10⁻³ mol/(min·L·sec), by(20^(2.51)/2^(4.51))×(Y/500). The use of the above supply of AsH₃molecules per unit time and per unit volume and the above supply of Heatoms per unit time and per unit volume allows the spreading resistanceof a fin side surface to be low, such as less than 6.3×10⁴Ω.

Similarly, the supply of AsH₃ molecules per unit time and per unitvolume needed to allow the spreading resistance to be less than or equalto 3.6×10⁴Ω when the SP is Y (W) is8.7×10⁻⁸/((1.7^(2.51)/2^(4.51))×(Y/500)) (mol/(min·L·sec)), which isobtained by dividing the supply of AsH₃ molecules per unit time and perunit volume needed to allow the spreading resistance to be less than orequal to 3.6×10⁴Ω when the SP is 500 W, i.e., 8.7×10⁻⁸ mol/(min·L·sec),by (1.7^(2.51)/2^(4.51))×(Y/500). The supply of He atoms per unit timeand per unit volume needed to allow the spreading resistance to be lessthan or equal to 3.6×10⁴Ω when the SP is Y (W) is3.4×10⁻³/((20^(2.51)/2^(4.51))×(Y/500)) (mol/(min·L·sec)), which isobtained by dividing the supply of He atoms per unit time and per unitvolume needed to allow the spreading resistance to be less than 3.6×10⁴Ωwhen the SP is 500 W, i.e., 3.4×10⁻³ mol/(min·L·sec), by(20^(2.51)/2^(4.51))×(Y/500). The use of the above supply of AsH₃molecules per unit time and per unit volume and the above supply of Heatoms per unit time and per unit volume allows the spreading resistanceof a fin side surface to be lowest, such as less than 3.6×10⁴Ω.

[Upper Limit of Supply of AsH₃ Molecules]

The desired upper limit of the supply of AsH₃ molecules per unit timeand per unit volume will be described hereinafter with reference to thedrawings.

First, in order to examine the influence of the supply of AsH₃ moleculeson the amount of As introduced into a fin side surface, samples wereevaluated using the condition E and new conditions I, J, and K withdifferent supplies of AsH₃ molecules.

The condition E was such that the AsH₃ concentration in the material gaswas 0.05% by mass, the He concentration was 99.95% by mass, and thetotal flow rate of a combination of He and AsH₃ was 475 cm³/min(standard state). As described above, this condition is equal to asituation where the supply of AsH₃ molecules per unit time and per unitvolume is 9.20×10⁻⁸ mol/(min·L·sec), and the supply of He atoms per unittime and per unit volume is 3.59×10⁻³ mol/(min·L·sec).

The condition I was such that the AsH₃ concentration in the material gaswas 0.5% by mass, the He concentration was 99.5% by mass, and the totalflow rate of a combination of He and AsH₃ was 475 cm³/min (standardstate). This condition is equal to a situation where the supply of AsH₃molecules per unit time and per unit volume is 9.25×10⁻⁷mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume is 3.59×10⁻³ mol/(min·L·sec).

The condition J was such that the AsH₃ concentration in the material gaswas 1.0% by mass, the He concentration was 99.0% by mass, and the totalflow rate of a combination of He and AsH₃ was 475 cm³/min (standardstate). This condition is equal to a situation where the supply of AsH₃molecules per unit time and per unit volume is 1.86×10⁻⁶mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume is 3.58×10⁻³ mol/(min·L·sec).

The condition K was such that the AsH₃ concentration in the material gaswas 3.0% by mass, the He concentration was 97.0% by mass, and the totalflow rate of a combination of He and AsH₃ was 475 cm³/min (standardstate). This condition is equal to a situation where the supply of AsH₃molecules per unit time and per unit volume is 5.68×10⁻⁶mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume is 3.59×10⁻³ mol/(min·L·sec).

Furthermore, the flat principal surface of a silicon substrate used as asample was examined by using a new condition L.

The condition L was such that the AsH₃ concentration in the material gaswas 5.0% by mass, the He concentration was 95.0% by mass, and the totalflow rate of a combination of He and AsH₃ was 475 cm³/min (standardstate). This condition is equal to a situation where the supply of AsH₃molecules per unit time and per unit volume is 9.66×10⁻⁶mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume is 3.57×10⁻³ mol/(min·L·sec).

The above-described conditions are all such that the material gas isAsH₃ diluted with He, the source power (the plasma-generatinghigh-frequency power) is 500 W, the bias voltage Vpp is 250 V, thesubstrate temperature is 22° C., the plasma doping time is 60 seconds,and the chamber volume is 93 L.

Each sample was subjected to plasma doping under the above correspondingcondition, and then subjected to annealing (specifically, spike RTA at1025° C.), and thereafter, the spreading resistance and erosion on a fincorner portion were measured by SSRM and SEM observation, respectively.Furthermore, the flat principal surfaces of silicon substrates weresubjected to plasma doping under the above corresponding conditionsseparately, the silicon substrates were then subjected to annealing(specifically, spike RTA at 1025° C.), and thereafter, the sheetresistances were measured using a four-point probe technique.

Consequently, under each of the conditions, the sheet resistance, thespreading resistance of the fin top surface, the spreading resistance ofa fin side surface, and the amount of increase in the radius ofcurvature of a fin corner portion were obtained as described below.However, under the condition L, only the flat principal surface of thecorresponding silicon substrate was examined.

Under the condition E, the sheet resistance was 500 Ω/sq., the spreadingresistance of the fin top surface was 1.1×10⁴Ω, the spreading resistanceof the fin side surface was 3.3×10⁴Ω, and the amount of increase in theradius of curvature of a fin corner portion was 2.0 nm.

Under the condition I, the sheet resistance was 340 Ω/sq., the spreadingresistance of the fin top surface was 3.0×10³Ω, the spreading resistanceof the fin side surface was 7.5×10³Ω, and the amount of increase in theradius of curvature of a fin corner portion was 1.2 nm.

Under the condition J, the sheet resistance was 342 Ω/sq., the spreadingresistance of the fin top surface was 3.6×10³Ω, the spreading resistanceof the fin side surface was 9.1×10³Ω, and the amount of increase in theradius of curvature of a fin corner portion was 1.5 nm.

Under the condition K, the sheet resistance was 345 Ω/sq., the spreadingresistance of the fin top surface was 2.6×10³Ω, the spreading resistanceof the fin side surface was 8.1×10³Ω, and the amount of increase in theradius of curvature of a fin corner portion was 3.7 nm.

Under the condition L, the sheet resistance measured on the flatprincipal surface of the silicon substrate was unstable, thereby makingthe formation itself of an impurity layer difficult.

FIG. 12 is a table providing a summary of the conditions described aboveand the results obtained under these conditions. As illustrated in FIG.12, on the conditions E, I, J, K, and L, parameters other than thesupply of AsH₃ molecules per unit time and per unit volume were set atsubstantially the same values, and the supply of AsH₃ molecules per unittime and per unit volume was varied within the range of greater than orequal to 9.20×10⁻⁸ mol/(min·L·sec) and less than or equal to 9.66×10⁻⁶mol/(min·L·sec).

FIG. 13 illustrates the relationship between the supply of AsH₃molecules per unit time and per unit volume under each of the conditionsE, I, J, and K and the sheet resistance measured on the flat principalsurface of the corresponding silicon substrate. Here, the sheetresistance measured on the flat principal surface of the siliconsubstrate can be estimated to be identical with the sheet resistance ofthe fin top surface. As illustrated in FIG. 13, when the supply of AsH₃molecules per unit time and per unit volume was increased in the rangeof greater than or equal to 9.20×10⁻⁸ mol/(min·L·sec), the sheetresistance of the fin top surface decreased. However, when the supply ofAsH₃ molecules per unit time and per unit volume reached 9.25×10⁻⁷mol/(min·L·sec), the decrease in the sheet resistance of the fin topsurface was saturated. The sheet resistance of the fin top surface waslow and stable in the range in which the supply of AsH₃ molecules perunit time and per unit volume was greater than or equal to 9.25×10⁻⁷mol/(min·L·sec). However, when the supply of AsH₃ molecules wasincreased to 9.66×10⁻⁶ mol/(min·L·sec), this caused a phenomenon inwhich the sheet resistance of the fin top surface significantly variedamong samples, and was unstable. A possible cause of this phenomenon isthat a thick deposition layer of arsenic was formed on the siliconsurface by excessively increasing the supply of AsH₃ molecules. Since,in particular, arsenic tends to be oxidized by being exposed to theatmosphere, a thick oxide of arsenic was probably formed on the siliconsurface, leading to variations in the sheet resistance.

FIG. 14 illustrates the relationship between the supply of AsH₃molecules per unit time and per unit volume under each of the conditionsE, I, J, and K and the spreading resistance of a fin side surface. Asillustrated in FIG. 14, similarly to the case illustrated in FIG. 13,when the supply of AsH₃ molecules per unit time and per unit volume wasincreased in the range of greater than or equal to 9.20×10⁻⁸mol/(min·L·sec), the spreading resistance of the fin side surfacedecreased. However, when the supply of AsH₃ molecules per unit time andper unit volume reached 9.25×10⁻⁷ mol/(min·L·sec), the decrease in thespreading resistance of the fin side surface was saturated. Thespreading resistance of the fin side surface was low and stable in therange in which the supply of AsH₃ molecules per unit time and per unitvolume was greater than or equal to 9.25×10⁻⁷ mol/(min·L·sec).

As described above, after considering all the results illustrated inFIGS. 13 and 14, when the supply of AsH₃ molecules per unit time and perunit volume is set greater than or equal to at least 9.20×10⁻⁸mol/(min·L·sec), the sheet resistance of the fin top surface and thespreading resistance of a fin side surface can be controlled to lowlevels. In particular, when the supply of AsH₃ molecules per unit timeand per unit volume is set in the range of greater than or equal to9.25×10⁻⁷ mol/(min·L·sec) and less than 9.66×10⁻⁶ mol/(min·L·sec), thesheet resistance of the fin top surface and the spreading resistance ofthe fin side surface can be extremely low and stable. However, when thesupply of AsH₃ molecules per unit time and per unit volume is setgreater than or equal to 9.66×10⁻⁶ mol/(min·L·sec), the followingphenomenon occurs: arsenic is excessively deposited in an amountexceeding the acceptable amount, thereby making the sheet resistance ofthe fin top surface unstable. For a similar reason, it is estimated thatwhen the supply of AsH₃ molecules per unit time and per unit volume isset greater than or equal to 9.66×10⁻⁶ mol/(min·L·sec), the spreadingresistance of the fin side surface is also unstable.

Therefore, the supply of AsH₃ molecules per unit time and per unitvolume is preferably set less than 9.66×10⁻⁶ mol/(min·L·sec). Similarlyto the above section “Influence of Source Power on Threshold Supply ofAsH₃ Molecules and Threshold Supply of He Atoms,” in consideration ofthe source power dependence, when the source power is Y (W), the supplyof AsH₃ molecules per unit time and per unit volume is preferably setless than 9.66×10⁻⁶/((1.7^(2.51)/2^(4.51))×(Y/500)) mol/(min·L·sec).

[Upper Limit of Amount of He Atoms]

The desired upper limit of the amount of He atoms per unit time and perunit volume will be described hereinafter with reference to thedrawings.

The supply of He atoms is determined by the internal chamber pressure,the exhaust capacity of the chamber, and the chamber volume. A casewhere the exhaust capacity of the chamber is 2700 L/second, and thechamber volume is 93 L will be described hereinafter as an example.

FIG. 11 shows that the use of the supply of He atoms allowing theinternal chamber pressure to be less than or equal to 0.6 Pa can reduceerosion (chipping of a fin corner portion) to a low level of less than 4nm. This enables the formation of a triple gate FET. Here, the supply ofHe atoms per unit time and per unit volume allowing the internal chamberpressure to be 0.6 Pa is 3.8×10⁻³ mol/(min·L·sec). The supply of Heatoms per unit time and per unit volume allowing the internal chamberpressure to be 0.6 Pa hardly varies even when the supply of AsH₃molecules per unit time and per unit volume varies within the range ofless than or equal to 1×10⁻⁵ mol/(min·L·sec).

Therefore, the supply of He atoms per unit time and per unit volume ispreferably set less than or equal to 3.8×10⁻³ mol/(min·L·sec).

Incidentally, when a double gate FET in which the fin top surface iscovered with a hard mask is formed, the fin top surface is protected bythe hard mask, thereby relaxing restrictions on the condition determinedunder consideration of erosion. Specifically, the desired upper limit ofthe supply of He atoms is greater than that when a triple gate FET isformed. Therefore, in order to examine desired conditions for forming adouble gate FET, a sample was evaluated using a new condition M.

The condition M was such that the AsH₃ concentration in the material gaswas 0.14% by mass, the He concentration was 99.86% by mass, and thetotal flow rate of a combination of He and AsH₃ was 800 cm³/min(standard state). This condition is equal to a situation where thesupply of AsH₃ molecules per unit time and per unit volume is 3.26×10⁻⁷mol/(min·L·sec), and the supply of He atoms per unit time and per unitvolume is 4.66×10⁻³ mol/(min·L·sec). Furthermore, the condition M issuch that the material gas is AsH₃ diluted with He, the source power(the plasma-generating high-frequency power) is 500 W, the bias voltageVpp is 250 V, the substrate temperature is 22° C., the plasma dopingtime is 60 seconds, the chamber volume is 93 L, and the internal chamberpressure is 1.2 Pa.

The sample was subjected to plasma doping under the condition Mdescribed above, and then subjected to annealing (specifically, spikeRTA at 1025° C.), and thereafter, the spreading resistance and erosionon a fin corner portion were measured by SSRM and SEM observation,respectively. Furthermore, the flat principal surface of a siliconsubstrate was subjected to plasma doping using the condition Mseparately, the silicon substrate was then subjected to annealing(specifically, spike RTA at 1025° C.), and thereafter, the sheetresistance was measured using a four-point probe technique.

Consequently, under the condition M, the sheet resistance, the spreadingresistance of the fin top surface, the spreading resistance of a finside surface, and the amount of increase in the radius of curvature of afin corner portion were obtained as described below.

Specifically, under the condition M, the sheet resistance was 348 Ω/sq.,the spreading resistance of the fin top surface was 3.4×10³Ω, thespreading resistance of the fin side surface was 2.9×10³Ω, and theamount of increase in the radius of curvature of the fin corner portionwas 11.8 nm.

Here, it should be noted that the spreading resistance of the fin sidesurface is lower than the spreading resistance of the fin top surface.The supply of AsH₃ molecules per unit time and per unit volume under thecondition M is 3.26×10⁻⁷ mol/(min·L·sec), and this value is at a levelbetween the supply of AsH₃ molecules per unit time and per unit volumeunder the condition E and the supply of AsH₃ molecules per unit time andper unit volume under the condition I. When the supply of He atoms perunit time and per unit volume is set at 3.59×10⁻³ mol/(min·L·sec) equalto that under each of the conditions E and I with the above supply ofAsH₃ molecules per unit time and per unit volume employed, the spreadingresistance of a fin side surface is reduced only to approximately1×10⁴-2×10⁴Ω. By contrast, under the condition M, the supply of He atomswas increased to 4.66×10⁻³ mol/(min·L·sec), which is approximately 30%greater than under each of the conditions E and I. This enabled asignificant reduction in the spreading resistance of a fin side surfaceto 2.9×10³Ω. However, erosion is increased to 11.8 nm as describedabove. Also in this case, when, in a double gate FET, the thickness of ahard mask covering the fin top surface is set at, e.g., approximately 30nm, this can prevent fin-type semiconductor regions themselves frombeing chipped.

Therefore, when a double gate FET is formed, the supply of He atoms perunit time and per unit volume may be set at 4.66×10⁻³ mol/(min·L·sec).

However, when the supply of He atoms per unit time and per unit volumeis set at 4.66×10⁻³ mol/(min·L·sec), the spreading resistance of a finside surface has already reached a lower level than the spreadingresistance of the fin top surface. Therefore, even when the supply of Heatoms per unit time and per unit volume is greater than 4.66×10⁻³mol/(min·L·sec), a further reduction in the spreading resistance of thefin side surface cannot be expected. Meanwhile, in this case, thefollowing adverse effect occurs: erosion becomes large enough to fail tobe prevented by a hard mask covering the fin top surface of a doublegate FET.

As described above, when a double gate FET is formed, the supply of Heatoms per unit time and per unit volume is preferably set less than orequal to 4.66×10⁻³ mol/(min·L·sec).

Although a case where the chamber volume is 93 L was described above asan example, a case where the chamber volume is 37 L will be describedbelow as an example.

In this case, the supply of He atoms per unit time and per unit volumeallowing the internal chamber pressure to be 0.6 Pa is 2.7×10⁻²mol/(min·L·sec). Specifically, when the chamber volume is 37 L, erosioncan be reduced to a low level of less than or equal to 4 nm, by settingthe supply of He atoms per unit time and per unit volume at 2.7×10⁻²mol/(min·L·sec) or less.

When the chamber volume is small, the gas residence time increases evenwith an increase in the internal chamber pressure unless the exhaustcapacity of the chamber is increased. This makes it difficult tosignificantly increase the supply of He atoms. For example, when thechamber volume is 37 L, and the internal chamber pressure is set at 0.9Pa, the supply of He atoms is substantially greatest, i.e., 2.84×10⁻²mol/(min·L·sec). In this case, the spreading resistance of a fin sidesurface is lowest. Furthermore, even when the adjustment of the exhaustcapacity of the chamber, etc., can slightly increase the supply of Heatoms, the supply of He atoms can be increased only up to 3×10⁻²mol/(min·L·sec). Therefore, when a double gate FET is formed, the supplyof He atoms per unit time and per unit volume is preferably less than orequal to 3×10⁻² mol/(min·L·sec). In order to allow the supply of Heatoms per unit time and per unit volume to be greater than 3×10⁻²mol/(min·L·sec), an increase in the size of an exhaust pump, etc., isrequired, thereby causing a problem where the size of a systemincreases.

While the upper limit of the supply of He atoms is dependent on thechamber volume, it is efficient to generally use a value in the chambervolume range of greater than or equal to 30 L and less than or equal to100 L as the chamber volume for use in plasma doping assumed in thisembodiment. When the chamber volume is less than 30 L, and a300-mm-diameter wafer is placed in the chamber, the inside diameter ofthe chamber is approximately equal to the diameter of the wafer. Thiscauses nonuniform gas flow, and thus, the dose tends to significantlyvary across the wafer surface. By contrast, when the chamber volume isgreater than 100 L, the chamber volume is too large to be economicallyefficient.

Based on such a chamber volume range, it is seen from the abovedescription that when a double gate FET is formed using a chamber havinga relatively small volume (greater than or equal to 30 L and less thanor equal to 65 L) in this embodiment, the supply of He atoms per unittime and per unit volume is preferably set less than or equal to 3×10⁻²mol/(min·L·sec). Here, similarly to the above section “Influence ofSource Power on Threshold Supply of AsH₃ Molecules and Threshold Supplyof He Atoms,” in consideration of the source power dependence, when thesource power is Y (W), the supply of He atoms per unit time and per unitvolume is preferably set less than or equal to3×10⁻²/((20^(2.51)/2^(4.51))×(Y/500)) mol/(min·L·sec).

When a triple gate FET is formed using a chamber having a relativelysmall volume (greater than or equal to 30 L and less than 65 L), thesupply of He atoms per unit time and per unit volume is preferably setless than or equal to 2.7×10⁻² mol/(min·L·sec). Here, similarly to theabove section “Influence of Source Power on Threshold Supply of AsH₃Molecules and Threshold Supply of He Atoms,” in consideration of thesource power dependence, when the source power is Y (W), the supply ofHe atoms per unit time and per unit volume is preferably set less thanor equal to 2.7×10⁻²/((20^(2.51)/2^(4.51))×(Y/500)) mol/(min·L·sec).

When a double gate FET is formed using a chamber having a relativelylarge volume (greater than or equal to 65 L and less than or equal to100 L), the supply of He atoms per unit time and per unit volume ispreferably set less than or equal to 4.66×10⁻³ mol/(min·L·sec). Here,similarly to the above section “Influence of Source Power on ThresholdSupply of AsH₃ Molecules and Threshold Supply of He Atoms,” inconsideration of the source power dependence, when the source power is Y(W), the supply of He atoms per unit time and per unit volume ispreferably set less than or equal to4.66×10⁻³/((20^(2.51)/2^(4.51))×(Y/500)) mol/(min·L·sec).

When a triple gate FET is formed using a chamber having a relativelylarge volume (greater than or equal to 65 L and less than or equal to100 L), the supply of He atoms per unit time and per unit volume ispreferably set less than or equal to 3.8×10⁻³ mol/(min·L·sec). Here,similarly to the above section “Influence of Source Power on ThresholdSupply of AsH₃ Molecules and Threshold Supply of He Atoms,” inconsideration of the source power dependence, when the source power is Y(W), the supply of He atoms per unit time and per unit volume ispreferably set less than or equal to3.8×10⁻³/((20^(2.51)/2^(4.51))×(Y/500)) mol/(min·L·sec).

1-18. (canceled)
 19. A semiconductor device comprising: a fin-typesemiconductor region formed on a substrate; and an n-type impurityregion formed in a side of the fin-type semiconductor region, wherein aspreading resistance of the n-type impurity region is less than9.0×10⁴Ω.
 20. The semiconductor device of claim 19, wherein thespreading resistance of the n-type impurity region is less than or equalto 6.3×10⁴Ω.
 21. The semiconductor device of claim 20, wherein thespreading resistance of the n-type impurity region is less than or equalto 3.6×10⁴Ω.
 22. The semiconductor device of claim 19, wherein then-type impurity region contains As.
 23. The semiconductor device ofclaim 19, wherein the n-type impurity region is an extension region, anda gate electrode is formed to cover a part of the fin-type semiconductorregion adjacent to the n-type impurity region.
 24. The semiconductordevice of claim 19, wherein the n-type impurity region is a source/drainregion, a gate electrode is formed to cover a part of the fin-typesemiconductor region apart from the n-type impurity region, and aninsulative sidewall spacer is formed to cover a side of the gateelectrode and a portion of the fin-type semiconductor region locatedbetween the n-type impurity region and the gate electrode.
 25. Thesemiconductor device of claim 19, wherein a width of the fin-typesemiconductor region along a gate width is less than or equal to 15 nm.